The correct answer is Presentation, which is Layer 6 of the OSI model. According to the CompTIA Network+ N10-009 objectives, the Presentation layer is responsible for data formatting, compression, and encryption, ensuring that data sent from the application layer of one system can be properly interpreted by the receiving system.

End-to-end encryption refers to encrypting data before transmission and decrypting it only at the final destination, preventing intermediaries from accessing the plaintext data. In the OSI model, this encryption and decryption function is logically placed at the Presentation layer, which sits between the Application and Session layers. This layer transforms data into a standardized format and applies security mechanisms such as encryption algorithms.

While modern implementations like TLS/SSL often operate across multiple layers in real-world networking stacks, the Network+ exam adheres to the conceptual OSI model when testing knowledge. From an OSI perspective, encryption is explicitly associated with the Presentation layer.

The Application layer provides network services to end-user applications, the Session layer manages session establishment and teardown, and the Transport layer focuses on segmentation, flow control, and reliability. None of these layers are primarily responsible for encryption within the OSI framework.

CompTIA emphasizes understanding these conceptual responsibilities, making Presentation the correct and expected answer.